I heard an old saying awhile back, that a Mustang stallion is the most dangerous prey animal in existence because they attack to kill when provoked. They know where the throat is, and they aim for it with intent to kill. Most other prey animals will batter you around until you're no longer a threat, which often can result in death, but horses can be particularly vicious when threatened.
I've heard horror stories of horses on the fight and the damage they can do. I won't lie, this video gave me immense pleasure. It always does when animals fight back. Death was likely all that was awaiting them anyway, so at least they got their final kicks in!